I also am skeptical, however WIRED did an interesting review. While the article doesn't include measurements it does speak to a lot of the "science" and engineering behind the design, including the techniques behind the low frequency response from the small displacement.
Again while they don't have any independent measurements I have always found WIRED to be a legitimate publication and I do trust them more then I do others.
http://www.wired.com/2015/06/review-devialet-phantom-2/
In general, this "review" seems like regurgitation of the Company's hype sheet.
Most science they present is "fun facts" type stuff with little associating their implementation with actual performance.
Here is their explanation of how they get deep bass out of this speaker:
To summon this low-frequency voodoo, engineers had to gin up the air pressure inside the Phantom to 20 times what is found in the average high-end speaker. “This pressure is equivalent to 174dBSPL, which is the acoustic pressure level associated with a rocket at launch…” reads the white sheet. For anyone curious, the rocket in question is a Saturn V.
More hype? Not as much as you might think. Which is why the speaker domes inside the Phantom’s extreme vacuum are fashioned from aluminum instead of any of the usual newfangled driver materials (hemp, silk, beryllium). Early prototypes fitted with the most robust commercial drivers available imploded upon liftoff, their diaphragms fragmenting into hundreds of itty-bitty pieces. So Devialet decided to make all their speakers out of 5754 aluminum (as thin as 0.3mm), the same alloy used to make welded nuclear tanks.
That really doesn't explain any of the science behind it.
From the manufacturer's website:
BANDWIDTH
16Hz to 25kHz ± 2dB at 82dB SPL | 28Hz to 25kHz ± 2dB at 92dB SPL | 49Hz to 25kHz ± 2dB at 102dB SPL
I appreciate that they are showing the bass drop off as you turn up the volume. I would assume these are at 1 meter distance so how loud would it be at 3-4 meters where you are more likely to be listening?
I don't trust their accuracy because they engage in plenty of mis-information. They say this speaker has 0 distortion, but when you go to the spec sheet they list
amplification distortion at 0.001%. That is impressive (though they provide no indication of at what frequency or power output), but if you are selling a powered speaker, providing the amp distortion as if it is the speaker's distortion is ridiculous.